That level of effort wouldn't be necessary to establish the bonafides of his claim, KJ; there is a much simpler way.
He could show his last five or so years of tax returns to Nersessian who would then tell us the amount of gambling winnings, losses, and ultimately the amount of gambling profit the dawg claimed and paid income tax on.
He should provide copies of both his federal and his California returns, to see if they jive.
Given the fact that the dawg portrays himself as a savvy attorney, and as we all know practicing attorneys are not to be trusted, in addition to copies of the returns he should proffer the summary of same which IIRC one can get upon request from the IRS.